1. Field of the Invention
The invention relates to methods for aligning microdomains of block copolymers to chemical patterns that have a lower spatial frequency than the microdomains.
2. Description of Background
Patterns of ever smaller features having nanoscale critical dimensions (CD) allow denser circuitry to be created, thereby reducing overall production cost for electronic devices. Similarly, ever tighter pitches (i.e., feature spacing in a pattern) and smaller CDs are needed at each new technology node. Methods such as directed self-assembly of block copolymers (BCPs), in which the pitch of a pre-pattern defined by a lithography tool is subdivided, have been considered as potential candidates for extending the current lithography technique.
Two common methods used to guide self-assembly in BCP thin films are graphoepitaxy (FIG. 1A) and chemical epitaxy (FIG. 1B). In the graphoepitaxy method (FIG. 1A), self-organization of block copolymers is guided by pre-patterned substrates 100. Self-aligned lamellar BCPs can form parallel line-space patterns of different domains (120, 130) in the topographical trenches and enhance pattern resolution by subdividing the space of topographical patterns 110. FIG. 1A shows in schematic form directed self-assembly of block copolymers on topographical patterns. A topographically patterned substrate 100 with a neutral underlying surface and sidewalls that are preferentially wetted by one type of the block copolymer domain (for example, the A domains of an A-B diblock copolymer assembly) can be used to direct self-assembly inside the trench through topographical confinement. With a trench of width L and BCP with a periodicity of PBCP, frequency multiplication of a factor of L/PBCP can be achieved for the remaining domain 130 after etch; however, defects and line-edge roughness are easily induced in this directed self-assembly scheme. If the sidewalls are neutral, the lamellae tend to orient perpendicular to the sidewalls and will not subdivide the pitch along the desired direction.
In the chemical epitaxy method, the self-assembly of BCP domains is guided by dense chemical patterns with the same dimension on the substrate (PS˜PBCP). The affinity between the chemical patterns and at least one of the types of BCP domains results in the precise placement of the different BCP domains on respective corresponding regions of the chemical patterns. (See FIG. 1B, which shows dense chemical patterns (111, 121) on a pre-patterned substrate 101, in which BCP domains 131 and 141 align to the chemical patterns, forming a pattern corresponding to the remaining domain 141 after etch.) The affinity for the one type of domain (for example the A domains of an A-B diblock copolymer assembly) dominates the interaction of the other domain(s) (for example the B domains) with the non-patterned regions of the surface, which can be selective or non-selective towards the other type(s) of domains. As a result, the pattern formation in the resulting BCP assembly directly mirrors the underlying chemical pattern (i.e., is a one-for-one reproduction of the features of the chemical pre-pattern. However, dimension control and line-edge roughness can be improved in such patterning methods by reducing variation in chemical pre-patterns. As a result, the pattern formation in the resulting BCP assembly directly mirrors the underlying chemical pattern (i.e., is a one-for-one reproduction of the features of the chemical pre-pattern).
Both graphoepitaxy and chemical epitaxy methods have been demonstrated. However, each of these two methods has limited use in generating patterns with high resolution and low CD variations, for different reasons. For example, in graphoepitaxy, the placement accuracy and edge roughness of BCP domains deteriorates during pattern formation due to variation in thickness uniformity of the over-coating of polymer film and due to imperfections in the topographical pre-patterns. The graphoepitaxy process also typically results in formation of a half-width domain next to each of the sidewalls so that the pattern spacing across the subdivided channel is not uniform. In addition, graphoepitaxy is very process intensive, requiring multiple fabrication steps (i.e., multiple lithographic patterning and etching steps) to create the topographic patterns and, frequently also requiring treatment to control the wetting properties of either the bottom or sidewalls of the patterns prior to performing the self-assembly process with a BCP. Chemical epitaxy on dense chemical patterns, though realizing a gain in CD control, provide no resolution enhancement when employing diblock copolymers. In addition, the 1:1 patterning of the chemical patterns at nanoscale feature sizes (100 nm or less) exceeds the capabilities of state-of-the-art optical lithography tools. Therefore, serial techniques like direct write e-beam lithography or parallel techniques like extreme-ultraviolet (EUV) interferometry are required. Patterning dense 1:1 features of this size with e-beam lithography is exceedingly difficult and requires enormous write times, making the throughput of the process too low (and the cost-of-ownership too high) to be practical. EUV interferometry remains an exotic technique with few production tools (especially EUV sources) available, suffers from similar throughput and cost-of-ownership issues, and has the typical practical limitations associated with interferometric techniques. Therefore, due to the aforementioned limitations, a directed self-assembly method to enhance resolution while reducing CD variation would therefore be highly desirable.